Atomistic Conversion Reaction Mechanism of WO3 in Secondary Ion Batteries of Li, Na, and Ca

Intercalation and conversion are two fundamental chemical processes for battery materials in response to ion insertion. The interplay between these two chemical processes has never been directly seen and understood at atomic scale. Here, using in situ HRTEM, we captured the atomistic conversion reaction processes during Li, Na, Ca insertion into a WO3 single crystal model electrode. An intercalation step prior to conversion is explicitly revealed at atomic scale for the first time for Li, Na, Ca. Nanoscale diffraction and ab initio molecular dynamic simulations revealed that after intercalation, the inserted ion–oxygen bond formation destabilizes the transition‐metal framework which gradually shrinks, distorts and finally collapses to an amorphous W and MxO (M=Li, Na, Ca) composite structure. This study provides a full atomistic picture of the transition from intercalation to conversion, which is of essential importance for both secondary ion batteries and electrochromic devices.The interplay between ion intercalation and WO3 battery electrode conversion was investigated at atomic scale by using in situ HRTEM. The ion–oxygen bond formation destabilizes the WO3 framework which gradually shrinks, distorts and finally collapses to an amorphous W and MxO (M=Li, Na, Ca) composite structure.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/135051/1/anie201601542.pdfhttp://deepblue.lib.umich.edu/bitstream/2027.42/135051/2/anie201601542-sup-0001-misc_information.pdfhttp://deepblue.lib.umich.edu/bitstream/2027.42/135051/3/anie201601542_am.pd

Atomistic Conversion Reaction Mechanism of WO3 in Secondary Ion Batteries of Li, Na, and Ca

Intercalation and conversion are two fundamental chemical processes for battery materials in response to ion insertion. The interplay between these two chemical processes has never been directly seen and understood at atomic scale. Here, using in situ HRTEM, we captured the atomistic conversion reaction processes during Li, Na, Ca insertion into a WO3 single crystal model electrode. An intercalation step prior to conversion is explicitly revealed at atomic scale for the first time for Li, Na, Ca. Nanoscale diffraction and ab initio molecular dynamic simulations revealed that after intercalation, the inserted ion–oxygen bond formation destabilizes the transition‐metal framework which gradually shrinks, distorts and finally collapses to an amorphous W and MxO (M=Li, Na, Ca) composite structure. This study provides a full atomistic picture of the transition from intercalation to conversion, which is of essential importance for both secondary ion batteries and electrochromic devices.Das Wechselspiel zwischen Ioneninterkalation und Umwandlung des WO3‐Elektrodenmaterials wurde durch In‐situ‐TEM auf atomarer Ebene untersucht. Die Bildung von Ion‐Sauerstoff‐Bindungen destabilisiert das WO3‐Gerüst: Es schrumpft, wird verzerrt und fällt schließlich zu einer amorphen W‐ und MxO‐Verbundstruktur (M=Li, Na, Ca) zusammen.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/134843/1/ange201601542_am.pdfhttp://deepblue.lib.umich.edu/bitstream/2027.42/134843/2/ange201601542.pdfhttp://deepblue.lib.umich.edu/bitstream/2027.42/134843/3/ange201601542-sup-0001-misc_information.pd

Unsupervised segmentation of irradiation\unicode{x2010}induced order\unicode{x2010}disorder phase transitions in electron microscopy

We present a method for the unsupervised segmentation of electron microscopy images, which are powerful descriptors of materials and chemical systems. Images are oversegmented into overlapping chips, and similarity graphs are generated from embeddings extracted from a domain\unicode{x2010}pretrained convolutional neural network (CNN). The Louvain method for community detection is then applied to perform segmentation. The graph representation provides an intuitive way of presenting the relationship between chips and communities. We demonstrate our method to track irradiation\unicode{x2010}induced amorphous fronts in thin films used for catalysis and electronics. This method has potential for "on\unicode{x2010}the\unicode{x2010}fly" segmentation to guide emerging automated electron microscopes.Comment: 7 pages, 3 figures. Accepted to Machine Learning and the Physical Sciences Workshop, NeurIPS 202

Spectroscopic Characterization of Aqua [ fac-Tc(CO)3]+ Complexes at High Ionic Strength.

Understanding fundamental Tc chemistry is important to both the remediation of nuclear waste and the reprocessing of nuclear fuel; however, current knowledge of the electronic structure and spectral signatures of low-valent Tc compounds significantly lags behind the remainder of the d-block elements. In particular, identification and treatment of Tc speciation in legacy nuclear waste is challenging due to the lack of reference data especially for Tc compounds in the less common oxidation states (I-VI). In an effort to establish a spectroscopic library corresponding to the relevant conditions of extremely high ionic strength typical for the legacy nuclear waste, compounds with the general formula of [ fac-Tc(CO)3(OH2)3- n(OH) n]1- n (where n = 0-3) were examined by a range of spectroscopic techniques including 99Tc/13C NMR, IR, XPS, and XAS. In the series of monomeric aqua species, stepwise hydrolysis results in the increase of the Tc metal center electron density and corresponding progressive decrease of the Tc-C bond distances, Tc electron binding energies, and carbonyl stretching frequencies in the order [ fac-Tc(CO)3(OH2)3]+ > [ fac-Tc(CO)3(OH2)2(OH)] > [ fac-Tc(CO)3(OH2)(OH)2]-. These results correlate with established trends of the 99Tc upfield chemical shift and carbonyl 13C downfield chemical shift. The lone exception is [ fac-Tc(CO)3(OH)]4 which exhibits a comparatively low electron density at the metal center attributed to the μ3-bridging nature of the -OH ligands causing less σ-donation and no π-donation. This work also reports the first observations of these compounds by XPS and [ fac-Tc(CO)3Cl3]2- by XAS. The unique and distinguishable spectral features of the aqua [ fac-Tc(CO)3]+ complexes lay the foundation for their identification in the complex aqueous matrixes

Resolving diverse oxygen transport pathways across Sr-doped lanthanum ferrite and metal-perovskite heterostructures

Perovskite structured transition metal oxides are important technological materials for catalysis and solid oxide fuel cell applications. Their functionality often depends on oxygen diffusivity and mobility through complex oxide heterostructures, which can be significantly impacted by structural and chemical modifications, such as doping. Further, when utilized within electrochemical cells, interfacial reactions with other components (e.g. Ni- and Cr-based alloy electrodes and interconnects) can influence the perovskite's reactivity and ion transport, leading to complex dependencies that are difficult to control in real-world environments. Here we use isotopic tracers and atom probe tomography to directly visualize oxygen diffusion and transport pathways across perovskite and metal-perovskite heterostructures, i.e. (Ni-Cr coated) Sr-doped lanthanum ferrite (LSFO). Annealing in 18O2(g) results in elemental and isotopic redistributions through oxygen exchange (OE) in the LSFO while Ni-Cr undergoes oxidation via multiple mechanisms and transport pathways. Complementary density functional theory (DFT) calculations at experimental conditions provide rationale for OE reaction mechanisms and reveal a complex interplay of different thermodynamic and kinetic drivers. Our results shed light on the fundamental coupling of defects and oxygen transport in an important class of catalytic materials.Comment: 39 pages, 10 figure